Characterization of pneumococcal secretion chaperones required for virulence Streptococcus pneumoniae is a Gram-positive pathogen that spreads through airborne droplets and colonizes the human nasopharynx where asymptomatic carriage is a prerequisite for invasive disease. S. pneumoniae is a significant health threat, globally causing more deaths than any other infectious disease. In order for S. pneumoniae to colonize and transition into an invasive infection, the bacterium relies on the elaboration of many virulence factors that are translocated across the bacterial membrane and destined for attachment to the cell wall or secretion into the host. Despite the pivotal importance of secreted proteins in bacterial pathogenesis, little is known about the mechanisms that regulate protein activity following membrane translocation in Gram-positive bacteria. Our laboratory identified the secretion chaperone PrsA2 in the Gram-positive bacterium Listeria monocytogenes (Lm) which is essential for virulence, and appears to be required for the proper folding and secretion of a number of virulence factors. My research has focused on the two prsA alleles of Lm: prsA1 and prsA2 that both have peptidyl-prolyl isomerase (PPIase) domains in addition to a foldase domain. We solved the crystal structure of Lm PrsA1 and I deciphered how structural features of PrsA1 and PrsA2 contribute to PPIase and chaperone activities in the organism. I have also determined that some PrsA activities are broadly conserved between species while others are highly specific. We recently solved the crystal structure of S. pneumoniae PrsA and I will use this structure to accomplish some of my research objectives to define the mechanisms that govern activity of secreted virulence factors in S. pneumoniae. Central to S. pneumoniae protein secretion are the surface exposed proteins: PrsA chaperone, HtrA protease/chaperone, and SlrA PPIase. I hypothesize that during host infection, S. pneumoniae PrsA, HtrA, and SlrA regulate proper folding, stabilization, and activity of secreted proteins which contribute to colonization and pathogenesis. In addition, surface exposed PrsA, HtrA and SlrA are potentially attractive drug targets because inhibition may increase antibiotic susceptibility while reducing virulence factor secretion. To implement my research objectives during the mentored K99 phase, I will work closely with my mentor Dr. Nancy Freitag who is an expert in the field of Gram-positive pathogenesis and my collaborator Dr. Don Morrison who is an expert in the field of S. pneumoniae molecular genetics and biology. By taking advantage of advances in proteomic analytical techniques, this award will enable me to establish a research program with the long-term objective of deciphering the mechanisms of virulence factor secretion and regulation in the Gram-positive pathogen S. pneumoniae which will also likely have broad relevance to other important Gram-positive pathogens.